A five-year study has found that depressed diabetics are at high risk of developing diabetic retinopathy, a disease that damages the eye's retina.
Diabetic retinopathy occurs when diabetes is not properly managed and is now the leading cause of blindness in patients between 25 and 74 years old, according to the study.
"Our study controlled for obesity, smoking, sedentary lifestyle and HbA1c levels, and still found that depression was associated with an increased risk of retinopathy," said co-author Wayne Katon, M.D.
HbA1c is a blood test that measures a person's average blood sugar levels over several months.
Katon and his colleagues studied 2,359 patients with diabetes enrolled in the Pathways Epidemiologic Study and assessed their levels of depression using the Patient Health Questionnaire-9 (PHQ-9), a self-reported survey of depression symptoms.
Over the five-year follow-up period, 22.9 percent of the patients who had PHQ-9 scores that ranked as "major depression" developed diabetic retinopathy, compared with 19.7 percent of the patients without depression.
With a five-point increase on the PHQ-9 score, patients' risk of having diabetic retinopathy increased by up to 15 percent.
"Our findings suggested that psychobiologic changes associated with depression such as increased cortisol levels and activity of blood-clotting factors may be linked to the development of retinopathy," Katon said.
The study has been published online in the journal General Hospital Psychiatry.